Emulsion polymers are widely used to bind nonwoven fibers into fabrics for use as facings or topsheets in diapers, bed pads, hospital gowns, and other such uses. The typical emulsion polymers for this use are prepared predominantly from ethylene, vinyl acetate, vinyl chloride and acrylate esters in combination with styrene or acrylonitrile, and use N-methylolacrylamide as the cross-linking agent. Although N-methylolacrylamide is widely used in the industry and provides excellent wet and dry tensile strength to the nonwoven fabrics, it suffers from two major drawbacks. N-methylolacrylamide is an equilibrium composition of acrylamide with free formaldehyde. Formaldehyde is a suspected carcinogen. A latex that uses N-methylolacrylamide as a latent crosslinking monomer will contain quantities of free formaldehyde, and consequently the nonwoven substrates bound with emulsion polymers containing N-methylolacrylamide will contain detectable quantities of free formaldehyde. In addition, acrylamide derivatives, including N-methylol acrylamide, are capable of undergoing strongly exothermic homopolymerization reactions, which makes processing, transportation and storage of acrylamides difficult.
The N-allyl-N-dialkoxyethylamide or amine monomer of the present invention is not in equilibrium with free formaldehyde, yet it provides latent crosslinking ability similar to the N-methylolacrylamide compounds. It also does not undergo strongly exothermic homopolymerization reactions.
U.S. Pat. No. 4,788,288, issued to Pinschmidt, Jr. et al., discloses N-olefinically substituted cyclic hemiamidals and hemiamide ketals, and N-olefinically substituted dialkyl acetals and ketals, which can be incorporated into free radical addition polymers to give formaldehyde-free compositions. U.S. Pat. No. 4,959,489 issued to Nordcuist et al. discloses a process for making an N-substituted acrylamide containing dialkyl acetal groups. However, the starting materials for some of these compositions are expensive and there is still a need for inexpensive formaldehyde-free compositions for use in emulsion binders for nonwoven fabrics.